Disposable puncturing units have been used to withdraw small quantities of blood from a body part (usually from a finger or earlobe) for analytical and diagnostic purposes. In this context, the puncturing units are typically designated as lancets. Lancets used for manual piercing are described, for example, in U.S. Pat. No. 3,789,830 and are typically only used by medically trained personnel. Nonetheless, the piercing can cause significant pain.
Puncturing instruments which contain a puncturing drive have been used for some time. The puncturing instrument may be a disposable item comprising a permanently integrated lancet. However, typically it is used several times and has a holder, by which a lancet may be replaceably coupled to the puncturing drive. Because the devices and lancets are elements which are mutually adapted and are provided by the same manufacturer, they are designated as a “puncturing system” or “blood withdrawal system.”
Usually a spring is used as the drive element and is located in a housing of the puncturing instrument. A lancet guide makes sure that the puncturing movement occurs along a predetermined movement path. At the beginning of development, very simple constructions of the drive were typical, in which the lancet was attached directly to one end of a spring inside an elongated housing. Such a puncturing system is disclosed, for example, in U.S. Pat. No. 4,469,110. Another early design of a puncturing instrument is described in U.S. Pat. No. 4,442,836 where the lancet moves in the direction toward the skin surface (forward phase of the puncturing movement) as it is driven by a first spring, while a second spring is used to drive the retraction of the lancet (retraction phase of the puncturing movement). The second spring is effective after the force coupling between the first spring and the lancet has been interrupted.
In typical designs, the puncturing instruments have an exit opening at their front end (in the piercing direction), from which the tip of the lancet exits to produce a wound in a body part, against which the front end of the puncturing instrument is pressed. The puncturing depth is defined by the distance in the piercing direction between the position of the lancet tip in the skin at the point the lancet stops moving forward (i.e., reversal point) and the plane of the skin contact area, which annularly surrounds the exit opening and contacts the skin at the instant of piercing. The front end of the puncturing instrument typically includes the skin contact area and thus forms a puncturing depth reference element which ensures that the puncturing depth has a predefined value.
To control the puncturing depth, it is typical to limit the movement of the lancet in the piercing direction by a stop connected to the lancet which hits a corresponding stop in the housing of the puncturing instrument. This housing-stop design is disclosed, for example, in U.S. Pat. No. 4,469,110. In the case of the drive comprising two springs described in U.S. Pat. No. 4,442,836, a defined position of the reversal point of the lancet is purportedly ensured by interrupting the force transmission between the drive spring and the lancet at a defined point along the movement path.
Blood withdrawal systems of this type do not meet the requirements that are necessary to regularly monitor analytical values of blood. This is true, in particular, for diabetics needing to frequently test their blood sugar level to keep it as close as possible within specific limits by adapting insulin injections to the demand (which varies substantially as a function of food intake, physical activity, etc.). It has been proven by extensive scientific work that the most severe late-stage damage caused by diabetes mellitus (for example, retinopathy with resulting blindness of the patient) may be dramatically reduced by intensive treatment using at least four blood analyses per day.
This intensive treatment requires that the blood withdrawal process cause the least possible pain. Great progress has been achieved in this regard by the design described in U.S. Pat. No. 5,318,584, which is based, inter alia, on the finding that the pain connected with obtaining blood may be significantly reduced if the puncturing system is made in such a manner that the piercing (even if new disposable lancets are used in each case for the piercing operations) is reproducible with better quality. To achieve this, a lancet drive having a drive rotor is used. A drive spring acts on one side of the rotor (drive side) and the other side (output-side) is coupled by a coupling mechanism to the lancet in such a manner that the rotation of the drive rotor is converted into the desired puncturing movement. The output-side coupling mechanism is designed (as a control curve) in such a manner that the lancet is coupled to the drive rotor essentially without play during the entire puncturing movement (comprising a forward phase and a retraction phase) whereby the lancet movement is completely controlled by the corresponding movement of the drive rotor. The shock caused by the abutting of the two stops in a drive type including housing stops (U.S. Pat. No. 4,469,110) is avoided in this design. In addition, due to the permanent coupling without play of the lancet to the drive rotor, an exactly reproducible position of the reversal point of the lancet movement during repeated puncturing movements is ensured, which was not achieved in the drive disclosed in U.S. Pat. No. 4,442,836.
The present invention relates to a puncturing system for withdrawing a body fluid, such as blood, from the skin. The puncturing system is an integrated system that not only withdraws fluid, but also analyzes the fluid by requiring a minimum of additional handling steps by the user. This causes additional requirements, which result from the limited space if both functions are to be performed in one device which (for handling reasons) must also be as small as possible.
Integrated systems are described in U.S. Pat. Nos. 5,029,583 and 5,514,152 in which the blood is obtained by a lancet needle, whose movement in the piercing direction is limited by a housing stop, as in U.S. Pat. No. 4,469,110. In U.S. Pat. No. 5,514,152, the generated blood droplet is transferred to an analysis sensor with the aid of a capillary channel running in the device housing.
U.S. Pat. No. 5,938,679 describes a puncturing system with a puncturing unit optionally provided with capillary tubes, through which blood may be suctioned into the interior of the device with the aid of capillary forces. This is an example of a puncturing system whose needle element has a capillary channel through which a body fluid may be transported from the skin into the interior of the puncturing unit. A further example of such a puncturing system is described in U.S. Publication No. 20030018282. The puncturing unit not only comprises the needle for piercing the skin, including a capillary channel for transporting the sample, but also a detection area containing reagents. Such a puncturing unit, which simultaneously has a receiving area for the sample (formed by a capillary-active absorption layer and/or hollow chamber) and preferably also contains the reagents required for the analysis, is designated hereinafter as a “microsampler.” Reference is made to the cited U.S. Publication No. 20030018282 and the documents cited therein, particularly U.S. Pat. No. 5,801,057, providing more specific details about microsamplers. Microsamplers of various designs may be used in the context of the present invention, taking into account the special features described above.
Embodiments of the present invention are generally directed to puncturing systems which include a needle element for piercing skin. The needle element can be solid or be a capillary needle (with an open capillary channel or the needle could be hollow with the capillary channel enclosed). The puncturing system produces puncturing depths suitable for use in integrated analysis systems.